Conventionally, in the manufacture of semiconductor devices, micro-processing by lithography using a photoresist composition has been carried out. The micro-processing is a processing method including forming a thin film of a photoresist composition on a silicon wafer, irradiating actinic rays such as ultraviolet rays through a mask pattern depicting a pattern for a semiconductor device, developing it to obtain a resist pattern, and etching the silicon wafer using the resist pattern as a protective film. However, in recent progress in high integration of semiconductor devices, there has been a tendency that shorter wavelength actinic rays are being used, i.e., KrF excimer laser beam (248 nm) and further ArF excimer laser beam (193 nm) have been taking the place of i-line (365 nm). Along with this change, influences of random reflection and standing wave off a substrate have become serious problems. Accordingly, it has been widely studied to provide an anti-reflective coating between the photoresist and the substrate (Bottom Anti-Reflective Coating, BARC).
As the anti-reflective coating, inorganic anti-reflective coatings made of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon or α-silicon and organic anti-reflective coatings made of a light-absorbing substance and a high molecular compound are known. The former requires an installation such as a vacuum deposition apparatus, a CVD (chemical vapor deposition) apparatus or a sputtering apparatus. In contrast, the latter is considered advantageous in that it requires no special installation so that many studies have been made. For example, mention may be made of the acrylic resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,919,599 and the novolak resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,693,691, and so on.
The physical properties desired for organic anti-reflective coating materials include high absorbance to light and radioactive rays, no intermixing with the resist layer (being insoluble in resist solvents), no diffusion of low molecular substances from the anti-reflective coating material into the topcoat resist upon coating or heat-drying, and a higher dry etching rate than the resist. They are described in, for example, Proc. SPIE, Vol. 3678, 174-185 and 800-809 (1999) and Proc. SPIE, Vol. 2195, 225-229 (1994).
Wiring delay has a more adverse effect on high-speed performance of LSI in LSI pattern rule having a fineness of 0.13 μm or less, and it becomes difficult to proceed an improvement in performance of LSI due to the present status of LSI process technique. Materials used for reducing wiring delay are a wiring material Cu and an interlayer insulating film having a low dielectric constant. And, a technique introduced for changing from Al (aluminum) as a wiring material to Cu is dual damascene process. The dual damascene process requires the use of an anti-reflective coating applied on a substrate having a larger aspect ratio (irregularity) compared with a substrate produced by using the conventional wiring material Al.
For anti-reflective coatings for dual damascene process, it is required to control a shape of an anti-reflective coating applied at the periphery of holes on a primary substrate. There are known the following two methods and anti-reflective coatings for controlling a shape of an anti-reflective coating applied at the periphery of holes on a primary substrate.
One of them is a method of full-fill type in which an anti-reflective coating is used in such a manner that holes are fully filled with the anti-reflective coating to make the surface of a substrate planarized. In this method, it is desirable to fill approximately 100% of holes with the anti-reflective coating. The merit of this method is advantages in lithographic process, while the demerit is disadvantages in etching process.
Another is a method of partial-fill type in which an anti-reflective coating is used in such a manner that holes are partially filled with the anti-reflective coating to cover the bottom parts and edge upper parts of the holes.
In this method, it is desirable that the filling rate of holes is around 20 to 80%. The merit of this method is advantages in semiconductor production that as the filling rate of holes is 20 to 80%, etching process for removing the anti-reflective coating can be carried out for a shorter time compared with a case where the filling rate of holes is approximately 100%. However, the demerit is disadvantages in lithography process in terms of an anti-reflective effect as a substrate having holes is not completely planarized. In addition, this method is generally used for substrates with a low integrated degree of a wiring width of 0.3 μm or more, because the method of partial-fill type often requires simultaneous use of another anti-reflective coating in order to use in a part of the substrate with a high integrated degree of a wiring width of 0.2 μm or less, unlike in the case where the anti-reflective coating in full-fill type is used in a part of the substrate with a high integrated degree of a wiring width of 0.2 μm or less.
As demand characteristics for the material for forming anti-reflective coating used in the partial-fill type, it is important to have the following performances when the anti-reflective coating is applied at a constant thickness:    (1) the filling amount of anti-reflective coating in holes is 20 to 80%, preferably 30 to 70% based on the volume of holes;    (2) the anti-reflective coating filled in holes has no void or gap;    (3) no anti-reflective coating is adhered to the side wall of holes;    (4) the edge upper part of the holes is covered with anti-reflective coating;    (5) anti-reflective coating has a constant thickness regardless of the density of holes on a substrate; and    (6) no resist poising occurs.The anti-reflective coating fully satisfying these six performances is needed.
In particular, materials for forming anti-reflective coating require the followings when an anti-reflective coating is applied at a constant thickness                the filling rate of holes with anti-reflective coating is 20 to 80%, preferably 30 to 70% based on the volume of holes;        no void or gap is present in holes; and        the anti-reflective coating has a constant thickness regardless of the density of holes on a substrate.        
As an example in which the conventional material for forming anti-reflective coating used in the partial-fill type is used, for example Japanese Patent Laid-open No. 2000-294504 discloses a method for forming photoresist relief image over a substrate having topography in which (a) a layer of anti-reflective composition containing a polymer having a molecular weight of about 8,000 or less is applied on the substrate; (b) a photoresist layer is applied on the layer of anti-reflective composition; and (c) the photoresist layer is exposed to an activated radiation, and the exposed photoresist layer is developed. The publication describes a preferable embodiment in which an anti-reflective composition exhibits a degree of planarization of about 0.5 or more for a step having slope shape formed by a local oxidation of silicon and a width of 0.8 μm and a depth at middle point of 2 μm. However, the publication does not describe the formation of void or gap of air that has a tendency to exert an adverse effect when the anti-reflective coating is applied and that is an important point in a case where the material for forming anti-reflective coating is used in partial-fill type, and nor describe whether or not the thickness of the anti-reflective coating is constant regardless of the density of holes on a substrate.
An object of the present invention is to provide a composition for forming anti-reflective coating for use in lithography which has a filling rate of holes with anti-reflective coating of 20 to 80% and no void or gap of air in the holes when the anti-reflective coating is applied at a constant thickness; gives an anti-reflective coating having a constant thickness regardless of the density of holes on the substrate; has a high prevention effect of reflected light; causes no intermixing with a resist layer; provide an excellent resist pattern; and has a higher dry etching rate compared with the resist, and to provide a method for forming resist pattern by using the composition for forming anti-reflective coating.
That is, polymers and compositions for forming anti-reflective coating disclosed in the present application are more appropriate for the anti-reflective coating of partial-fill type that is used to obtain anti-reflective performance and a high dry etching rate for applying to semiconductor devices having a relatively wide wiring width, rather than for the anti-reflective coating of full-fill type that is used to obtain anti-reflective performance by fully filling holes on a substrate and planarizing it for applying to semiconductor devices having a relatively narrow wiring width.